diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 2ea31db..945d404 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -328,7 +328,7 @@
     start_red=
     end_color=
     if [ -t 1 ]; then
-        case "$TERM" in
+        case "${TERM:-}" in
             *color*|cygwin|linux|rxvt*|screen|[Eex]term*)
                 start_red=$(printf '\033[31m')
                 end_color=$(printf '\033[0m')